The polymerization of 1,3-butadiene to form high cis-1,4-polybutadiene employing organonickel based catalyst systems has been described in several patents and publications.
In U.S. Pat. No. 3,856,764, issued Dec. 24, 1974, there is disclosed a process for producing cis-1,4-polybutadiene by contacting 1,3-butadiene with a catalyst consisting of (1) at least one organoaluminum compound, (2) at least one nickel compound selected from a class consisting of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel tetracarbonyl and (3) at least one hydrogen fluoride complex prepared by complexing hydrogen fluoride with one or more members of a class consisting of ketones, esters, ethers, alcohols, nitriles and water.
In U.S. Pat. No. 3,528,957, issued Sept. 15, 1970, there is described the solution polymerization of butadiene to form high cis polybutadiene which comprises polymerizing butadiene in the presence of an organometal compound of groups 1, 2, and 3 of the Periodic Table with particular emphasis to trialkyl aluminum compounds and (2) at least one compound from the class consisting of organonickel compounds, and (3) at least one boron trifluoride complex prepared by complexing boron trifluoride with a member of the class consisting of monohydric alcohols, phenols, water and mineral acids containing oxygen.
In U.S. Pat. No. 3,910,869 issued Oct. 7, 1975, there is disclosed a process for the polymerization of butadiene to form polymers containing a high proportion of the butadiene units in the cis-1,4 configuration which comprises contacting the butadiene under solution polymerization conditions with a catalyst comprising (1) an organoaluminum compound, (2) an organonickel compound and (3) hydrogen fluoride.
In U.S. Pat. No. 3,483,177, issued Dec. 9, 1969, there is disclosed a process for the polymerization of butadiene to form polybutadiene containing a high proportion of the butadiene units in the cis-1,4 configuration which comprises contacting butadiene under polymerization conditions with a catalyst comprising (1) at least one organometallic compound in which the metal is selected from Groups I, II, and III of the Periodic System; (2) at least one organometallic compound selected from the class of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel carbonyl; and (3) at least one boron trifluoride complex prepared by complexing boron trifluoride with a member of the class consisting of ketones, aldehydes, esters and nitriles.
In U.S. Pat. No. 4,020,255, issued Apr. 26, 1977, there is disclosed a process for preparing high cis-1,4-polybutadiene which comprises continuously polymerizing butadiene in an inert aliphatic or cycloaliphatic solvent using as a catalyst a mixture comprising (a) at least one trialkylaluminum wherein the alkyl group contains from 2 to 8 carbon atoms; (b) at least one nickel salt of a carboxylic acid; and (c) at least one boron trifluoride complex of ethers in which each of the individual catalyst components are continuously injected into the polymerization vessel containing the mixture of butadiene and inert solvent.
Furthermore, the polymers obtained from these polymerizations are of fairly high molecular weight in the neighborhood of 3.0 or greater than 3 DSV (dilute solution viscosity).
In U.S. Pat. No. 3,170,907, issued Feb. 23, 1965, there is disclosed a process for the conversion of butadiene to a solid polybutadiene polymer having a high content of cis-1,4-configuration by contact with a catalyst system comprising (a) a nickel salt of an organic acid, (b) a boron trifluoride etherate, and (c) an organometallic compound of aluminum.
One of the nickel based catalyst systems which have been described above which is of significant industrial importance is the one which employs a nickel carboxylate compound in conjunction with an organoaluminum compound and hydrogen fluoride or a hydrogen fluoride etherate.
The second most important industrial catalyst system based on nickel to catalyze polybutadiene is the system employing a nickel carboxylate in conjunction with an organoaluminum compound and boron trifluoride etherate. This system also yields extremely high cis-1,4-polybutadiene. However, the molecular weights are slightly lower than the system employing the hydrogen fluoride or hydrogen fluoride complexes.
In many applications of cis-1,4-polybutadiene, it is usually desirable to employ lower molecular weight polymers than those generally obtained from either one of the immediately aforementioned polymerization systems. For example, in certain tire applications it is desirable to use a high cis-1,4-polybutadiene having a DSV of about 3. On the other hand, if the high cis-1,4-polybutadiene is used in a sealant or in a paint, liquid polybutadienes are usually employed.
The invention described herein deals with the use of various hydrocarbon compounds as molecular weight regulators for the above-mentioned polybutadiene syntheses. The utilization of these molecular weight regulators expands the scope of the organoaluminum/organonickel/fluorine catalyzed 1,3-butadiene polymerization systems in a manner that they can be used for the synthesis of cis-1,4-polybutadiene ranging from an extremely high molecular weight elastomer to a liquid polymer. These syntheses of various molecular weight polybutadienes can readily be effected in an anionic or an emulsion polymerization system by the mechanism of the catalyst level or the chain transfer level, respectively. However, these polymerization systems do not yield high cis-1,4-structure typical of the aluminum/nickel/fluorine-based solution polymerizations mentioned above. For example, a typical alkyllithium initiated (anionic) 1,3-butadiene polymerization generally yields polymers containing 36-44 weight percent cis-1,4 polymer, 48-50 percent trans-1,4 polymer and 8-10 percent, 1,2 structures. On the other hand, a typical emulsion polymerization of butadiene yields a polymer containing about 60 percent trans-1,4 structure, about 20 percent cis-1,4 structure, and about 20 percent 1,2 structure.
Liquid polybutadienes have been synthesized using nickel compounds and alkylaluminum halides. However, these catalyst systems do not yield a very high cis-1,4-structure in the polybutadiene which is typical of the nickel carboxylate/aluminum alkyl/fluorine-containing systems, nor do they have the flexibility to yield high molecular weight polymers.
The uniqueness of the present invention is that it expands the scope of the high cis-1,4 directing 1,3-butadiene polymerization systems such that they can be employed for the synthesis of polymers ranging from an elastomer to an oily liquid.
The effect of certain hydrocarbon compounds on polymer intrinsic viscosity ([.eta.]) in 1,3-butadiene polymerization employing a nickel-based catalyst system was studied by Sakata et al, in Die Makromolekulare Chemie. 139 (1970) 73-81. These studies employed a triethyl aluminum/nickel carboxylate/boron trifluoride catalyst system in benzene solvent. The compounds screened in this study included saturated hydrocarbons, such as propane, n-butane and isobutane; alpha-olefins, such as propylene, butene-1, and isobutene; internal olefins, such as cis and trans butene-2 and concentrated diolefins, such as allene and 1,2-butadiene; acetylenes, such as acetylene, methylacetylene and vinylacetylene and a nonconjugated diolefin, 4-vinylcyclohexene-1. The authors of this paper concluded that saturated hydrocarbons and monoolefins, such as .alpha.-olefins and internal olefins show no effect on the polymer viscosity nor on the conversion. They found that 4-vinylcyclohexene has the effect of lowering the polymer viscosity, however, to do so required such an amount as to preclude its employment as a useful molecular weight regulator. The acetylenes did lower the molecular weight but they have a very dramatic, detrimental effect on polymer yield.
Another nickel-based catalyzed 1,3-polybutadiene system employing a molecular weight regulator is that reported by Ukita and and coworkers, in U.S. Pat. No. 3,725,492, issued Apr. 3, 1973. Ukita et al prepared liquid oligomeric polybutadienes containing about 70 percent cis-1,4-configuration by carrying out the butadiene polymerization by using R.sub.n AlCl.sub.3-n wherein R is an alkyl of 1--carbons, nickel salts of carboxylic acids, and water in the presence of 1-butene. These patentees produced a polymer which was in the nature of an oil and was liquid.